<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS-数据类型</title>
</head>
<body>

</body>
<script>

    //原始数据类型
    alert(typeof 3);
    alert(typeof 3.14);

    alert(typeof "A");
    alert(typeof 'Hello');

    alert(typeof true);
    alert(typeof false);

    alert(typeof null);

    var a ;
    alert(typeof a);
        
</script>
</html>